guest-diag: pin_sem_fast.sh - 2 s tracker-sem pinner with a per-pid guard

The 15 s pinner loses the race against the client's internal deadline in
most boots: in the one boot where UVM's page-table write pushes were
submitted the pin had landed early, and later pins (60 s+) left the client
dead before submitting anything. Poll the guest pagemap every 2 s and pin
0x20400f000 once per cdt pid (re-pinning the same pid also stirred the
pump's rewind repeatedly, which is why the guard exists).

1 files changed, 33 insertions, 0 deletions

diff --git a/tools/guest-diag/pin_sem_fast.sh b/tools/guest-diag/pin_sem_fast.sh
new file mode 100755
index 0000000..e0e30f8
--- /dev/null
+++ b/tools/guest-diag/pin_sem_fast.sh
@@ -0,0 +1,33 @@
+#!/bin/bash
+# pin_sem_fast.sh - low-latency tracker-sem pinner (2 s poll vs 15 s).
+#
+# Pins the client tracker-sem page (0x20400f000, covers 0x20400fec0..ff70)
+# for the live cdt pid the moment the guest pagemap shows it present, once
+# per pid. The window matters: in the one boot where UVM's page-table write
+# pushes were submitted, the pin had landed ~40 s before the client's
+# internal deadline; later pins (60 s+) lose the race and the client dies
+# without ever submitting the writes.
+#
+# Usage: tools/guest-diag/pin_sem_fast.sh [iterations]   (default 200, ~7 min)
+set -u
+cd "$(dirname "$(readlink -f "$0")")/../.."
+EXEC() { timeout 20 ./scripts/vgpu_vm.py exec --timeout 15 "$1" 2>/dev/null; }
+
+B64=$(base64 -w0 tools/guest-diag/guest_pmap_all.py)
+EXEC "echo '$B64' | base64 -d > /tmp/pmapall.py" >/dev/null
+
+N=${1:-200}
+pinned_pid=""
+for ((i = 1; i <= N; i++)); do
+    pid=$(EXEC 'pgrep -x cdt | head -1' | tail -1)
+    if [ -n "$pid" ] && [ "$pid" != "$pinned_pid" ]; then
+        line=$(EXEC "sudo python3 /tmp/pmapall.py $pid 0x20400f000 1" |
+            grep -aE "^0x20400f000,0x[0-9a-f]+$" | head -1)
+        if [ -n "$line" ]; then
+            echo "$line,0x1000,1" | sudo tee /sys/module/open_iov_vfio/parameters/sema_map_add >/dev/null
+            pinned_pid="$pid"
+            echo "[$((i * 2))s] pinned $line (pid $pid)"
+        fi
+    fi
+    sleep 2
+done
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